In metal stamping operations and apparatus, it is well-known to utilize a manifold cushion assembly having multiple separate cushion cylinders on the ram and/or bolster of a press to allow for use of multiple different dies without providing a dedicated manifold cushion assembly for each die. As shown in FIGS. 1 and 1A, the cushion apparatus comprises a plate-like manifold member M defined from steel or the like including gas-flow passages G drilled or otherwise formed therein. A plurality of cylinders C are operatively secured to the manifold M and are pressurized by nitrogen or other inert gas N held under high-pressure within the gas-flow passages G of the manifold. As used herein the term high-pressure is intended to mean a pressure of at least 300 pounds per square inch (psi) or at least 2068.5 kilopascal (kPa). As shown in FIG. 1A, each cylinder C comprises a metal body B including an inner wall BW that defines a bore BR. A metal piston P is slidably mounted within the bore BR and is adapted to reciprocate slidably in the bore axially a stroke distance S. The nitrogen or other inert gas contained in the passages G under pressure flows into the cylinder bore BR (see arrows N) and biases the piston P of each cylinder C to a normal, extended position as shown in FIG. 1, so that the piston P abuts a flange FB located at an outer end of the body B.
In use, a die is fitted over the cushion assembly (the cushion assembly comprises the manifold M and a plurality of cylinders C) and actuation pins of the die are aligned with the pistons P of at least some of the cylinders C. When the die portions are mated in the press to perform work, a die actuation pin engages an outer surface O of a piston P and strokes the piston axially inward for at least part of the stroke distance S against the pressure of the gas as indicated by the arrow A. As such, the cylinders C cushion the mating engagement of die portions in a press. Parting of the die portions is also facilitated owing to the biasing force exerted on the piston P by the pressurized gas contained in the manifold M.
With continuing reference to FIG. 1A, the body B of cylinder C is received in a mounting location bore MB of the manifold and is typically connected to the manifold M via mating threads T formed on the body and manifold or otherwise. An O-ring seal OS closely surrounds the cylinder body and sealingly engages the manifold M to prevent escape of gas between the body B and manifold M. The outer end of the body B includes a sleeve bushing E fitted thereon that closely received and surrounds the actuation pin of a die and guides same into engagement with the piston P.
The piston P is slidably supported in the bore BR by first and second axially spaced-apart annular bearings BE1,BE2. The first bearing BE1 is seated against an inward side of a flange FP of the piston. An annular seal member SL1 is located outwardly of the first bearing BE1 on the opposite side of the flange FP relative to first bearing BE1. The seal SL1 is seated against the piston P in a groove G1 and slidably engages the inner wall BW defining cylinder bore BR to prevent entry of metal particles or other contaminants therepast into bore BR. A second seal SL2 is located inwardly of the first bearing BE1 and is seated against first bearing BE1. The seal SL2 encircles piston P and slidably abuts the inner wall BW defining bore BR to prevent escape of gas N from passages G between piston P and body B in bore BR.
An annular spacer or carrier member SP defined from a metal such as aluminum or a polymeric material supports one or more annular wiper members SPW that slidably engage the inner wall BW defining bore BR. The wiper members SPW can be provided by foam members impregnated with oil so as to clean and lubricate inner wall BW when piston P reciprocates in bore BR. The second bearing BE2 axially abuts the inner end of spacer/carrier SP and is retained on piston P via snap-ring SN or the like.
The bearings BE1,BE2 are typically defined from a phenolic resin or the like. The seals SL1,SL2 are conventional polymeric seals and are typically U-cup seals or the like.
As noted, the bearings BE1,BE2 slidably support the piston P in the bore BR. As such, the bearings BE1,BE2 define inclusively therebetween an axial bearing-length L. The bearing-length L is the maximum axial distance between the outermost bearing (in this case BE1) and the innermost bearing (in this case BE2). In the case where only a single bearing member is used, the bearing-length L would correspond to the axial length of the single bearing member. The bore BR defines a diameter D. Heretofore, cylinders C for high-pressure inert gas cushion assemblies of the type described above as used for metal stamping have typically been manufactured with a ratio of bearing-length L to bore diameter D, L:D of about 1:1, i.e., in conventional cylinders C for high-pressure inert gas cushion assemblies, the bearing-length L has typically been at least nearly equal to or greater than the bore diameter D. Known cylinders of this type have not been provided with a L:D ratio of significantly less than 1:1, i.e., the dimension L has always been nearly equal to or greater than the dimension D. This has been found to be required with cylinders for high-pressure cushion assemblies, such as the cylinder C illustrated herein, to prevent jamming of the piston P in the bore BR or leakage of the high-pressure inert gas when the piston P is actuated under less than perfectly aligned conditions as are commonly encountered in use and which can cause tipping of the piston relative to the axis on which the piston P reciprocates. This can occur, e.g., when a metal chip becomes trapped between the die actuation pin and the piston P or due to misalignment. It should be noted that, unlike low-pressure cushion system that are continuously or periodically connected to a source of compressed air or “shop air,” the high-pressure inert gas cushion assemblies of the type just described are charged with the pressurized inert gas only periodically and must function for a very large number of cycles without leakage of the biasing gas.
Those of ordinary skill in the art will recognize that for a given required stroke distance S, maintaining an L:D ratio of about 1:1 or greater requires the overall height H of the cylinder C to be increased to accommodate the required length L of the piston P. In certain applications, however, it has been deemed desirable to reduce the overall height of a cylinder C while maintaining a constant stroke distance S. For example, in certain applications, it has been deemed desirable to minimize the height H of the cylinder so that the height of the manifold M and overall cushion assembly can be correspondingly reduced, thereby increasing the press-open space available for dies.